Paul Bacon, a solicitor who has represented defendants accused of joint enterprise murders, said the law can be "very unfair".

"I think it's drawing people in who would otherwise have been found not guilty. It makes it very difficult for those parties to prove their innocence," he said.

"This is one area where everybody who is involved in the justice system, the lawyers, the judges, the police, the prosecutors, are not comfortable with it. And because there's that element of 'Is this right?' we need clarification, we need guidance more than anything."

However, he said joint enterprise had helped convict people in some "very difficult" and "quite historic" cases, including the murder of Stephen Lawrence.